The dimensionless ratio of liquid gradient to pressure drop head caused by the bubble cap assembly should be less than 0.4
Tendency towards stable operation is increased by increasing the skirt clearance of the caps, lowering the rate of liquid flow per unit plate width or increasing the spacing between the caps
The pressure drop due to the caps & slots and the static submergence should be as high as practicable for reasonable operation
Distillation under vacuum is a substitute for steam distillation
In flash (equilibrium) distillation, a definite fraction of liquid is vaporised in such a way that the evolved vapour & residual liquids are in equilibrium with each other
Flash distillation, differential distillation & steam distillation are all continuous distillation processes
In differential (simple) distillation, the vapour is removed as soon as it is formed without appreciable condensation